Working fluids based on a silicone fluid as the principal constituent are hitherto used practically in various types of damper units but they are not quite satisfactory in performance because of the poor boundary lubrication of silicone fluids in gereral. For example, metal surfaces under friction with each other are subject to wearing when they are in contact with each other under revolution or vibration as in the damper units used in machines for transportation or power generators charged with a working fluid based on a silicone fluid as the major constituent so that the damper units are accompanied with a problem that the performance thereof is degraded by the increase in the consistency of the fluid caused by enterng of metallic dusts produced by abrasion. Another problem is caused by the heat of friction leading to increase in the fluid temperature so that rearrangement reaction may take place in the molecular chains of the silicone as is indicated by the viscosity decrease of the fluid consequently to cause a decrease of the output power of the damper unit below the initially desired level.
With an object to solve the above mentioned problems in silicone-based working fluids, a method has been proposed in which the silicone fluid is admixed with diesters such as dialkyl adipates, dialkyl sebacates, dialkyl azelates and the like, monoesters such as alkyl myristates, alkyl palmitates and alkyl ricinolates, dialkyl chlorendates and the like. Although the lubricity performance of a silicone fluid can indeed be improved by the addition of these additives as a consequence of their solubility to some extent in silicone fluids, a considerable increase in the temperature of the working fluid is sometimes unavoidable in the practical use thereof due to the heat of internal friction produced in the fluids per se even in the absence of wearing by friction on the metal surface so that such fluids are not serviceable as a silicone-based working fluid with a high degree of durability and heat resistance because of evaporation or decomposition due to thermal deterioration of such additives.
In addition, another proposal has been made to improve silicone fluids by adding molybdenum disulfide, which is a solid lubricant, though with an accompanying disadvantage that no stable fluid composition can be obtained thereby because of settling of the additive in the lapse of time after dispersion in the silicone fluid due to its high density of about 4.8 g/cm.sup.3.